Usually, laminates used in a PCB adopt a halogen flame retardant to prevent burning. When burning, these halogen flame retardants will send out not only a lot of fume that smells awful, but also will produce strong corrosive halogen hydride gases. Furthermore, according to literatures of recent years, halogen flame retardants will produce carcinogens, such as dioxin and dibenzofuran, during high-temperature splitting and burning. Therefore, with the EU directives on WEEE (Waste Electrical and Electronical Equipment) and RoHS (Restriction of Hazardous Substances in Electrical and Electronic Equipment) being put in practice in Jul. 1, 2006, developing halogen-free flame-retardant type laminates used in a PCB has become the key work of the industry.
On the other hand, PCBs are the key electronic part of portable electronic products, satellite transmission products, and communication products, and the performance of PCBs will directly influence the performance of the electronic products. However, the performance depends on the dielectric coefficient and the dielectric loss of the substrate to a great extent, since the signal transmission speed with the formula V=C/s and the loss power with the formula P=kft in a PCB are closely related with them. Thus, the relative dielectric constant is smaller, the transmission of the signal is faster; the dielectric dissipation factor is smaller, the frequency capable to be transmitted is higher when the loss power of the signal remains unchanged during the transmission process. That is, when the signal remains at the same frequency, the dielectric loss is smaller, the distortion rate during the signal transmission process is lower. So, with the development trend of electronic products being thinner, lighter, and smaller, and the transmission frequency being towards GHz (quasi-microwave band), it is very important to develop a new generation of PCB substrate with high performance for high frequency transmission.
In recent years, to improve the performance of the above mentioned copper clad laminate (CCL), the researchers have tried in many ways. It has been researched to adopt high performance resin matrix such as polytetrafluoroethylene resin, bismaleimide triazine resin, thermosetting poly(phenyleneoxide) resin, cyanate ester resin, polyimide, and polyetheretherketone. However, application of the above high performance resin matrix is limited by the factors such as processability and price. Developing epoxy group PCBs for high frequency transmission is the major research direction. Currently, only a few Japanese companies can produce such products. With the further development in communication and information industry such as satellite communication, personal computers, and mobile phones, the requirement to the performance of electronic products is more and more, and so developing an epoxy group PCB for high frequency transmission with comparatively low dielectric coefficient and dielectric loss is necessary.
Patents such as Belgian patent No. 627887, Chinese patent No. 1955219, U.S. Pat. No. 6,534,181B2, and U.S. Pat. No. 6,509,414B2 disclosed to use the copolymer of styrene-maleic anhydride (SMA) to cure epoxy resin. However, the material is inevitable to have a plenty of hydrophilic groups after epoxy resin is cured by anhydride, which results in comparatively large water absorption of the material. Thus, at the condition of high temperature and high humility, the cured epoxy resin is very sensitive to water. Besides, phosphorus-containing flame retardants easily absorb moisture.